An IEEE 802.1BR-based network topology (also known as an extended bridge) is a logical network entity that comprises two different types of units: a controlling bridge (CB) unit and one or more port extender (PE) units. The CB serves as the controller of the extended bridge and is responsible for performing control plane functions (e.g., Layer 2 switching, Layer 3 routing, etc.) with respect to network traffic passing through the bridge. In contrast the PEs, which connect to the CB and to other devices/hosts external to the extended bridge, act as non-intelligent devices and thus do not perform any local switching or routing; instead, their primary function is to provide additional data port terminations for the CB (thereby extending the port capacity of the CB). For example, each PE may be a switch/router with X number of physical data ports, which appear as virtual data ports on the CB. Upon receiving a data packet from an external device/host on an ingress data port, the PE forwards the data packet to the CB, which processes the data packet in hardware or software to determine an appropriate egress port through which the packet should be sent out. The CB then forwards the data packet to the PE housing the egress port for transmission through that port towards the next hop destination.
In some cases, an extended bridge may support multiple CBs which connect to each other according to a linear or ring topology. In these cases, one CB may be selected as the “master” CB of the extended bridge and serve as the central point of management for the entire bridge. Other CBs may operate in a “standby” or “member” mode.
The links that interconnect the PEs to each other and to the CB in an extended bridge are known as cascade links. Each cascade link comprises, at its endpoints, an upstream port (i.e., a port that provides connectivity towards the CB) and a downstream port (i.e., a port that provides connectivity down a PE chain). These upstream and downstream ports are collectively referred to herein as “cascade ports” of the cascade link. Generally speaking, cascade links are considered internal to the extended bridge since they only carry data traffic that has been tagged with a special ETAG header that is understood by the PEs and the CB. This ETAG header facilitates the internal routing of data traffic from an ingress PE to the CB for processing, as well as from the CB to the egress PE(s) that will forward traffic out of the extended bridge.
In order to properly handle ETAG traffic, the physical cascade ports at the endpoints of a cascade link need to be configured to operate in an ETAG-enabled mode instead of a conventional data port mode. This configuration is typically performed via an LLDP (Link Layer Discovery Protocol) based exchange between the CB and a given PE at the time the PE joins the extended bridge, and may be updated in response to dynamic port changes that are made during system runtime. In the past, each endpoint of a cascade link has generally been limited to being a single cascade port. However, in new emerging 802.1BR implementations, each endpoint of a cascade link may be a link aggregation group (LAG) that comprises multiple physical ports but is treated as a single logical port. In these cases, the cascade link may also be referred to as a cascade trunk. With these new implementations, novel techniques are needed to manage the configuration and reconfiguration of such LAGs.